Slaughter stopper

New vaccines could one day prevent the mass slaughter of livestock during foot and mouth outbreaks. Britain and other European countries are currently destroying tens of thousands of animals.

Conventional vaccines exist but animals given these can harbour the live virus for up to two years and pass it on to unvaccinated animals, says Alex Donaldson, head of the Institute for Animal Health in Pirbright, Surrey.

And if Britain resorted to vaccination, it wouldn't be able to export animals or animal products for at least this long. "That's a very considerable disadvantage," Donaldson says.

Infected or vaccinated?

The key problem is that conventional vaccines consist of inactivated copies of the foot and mouth disease virus. The antibodies produced against this are identical to those produced in an animal harbouring the live virus, making it difficult to tell one animal from the other.

But Marvin Grubman and his colleagues at the US Department of Agriculture's secure research facility on Plum Island, New York, are developing a vaccine that will make the job easier.

They have inserted the genes that code for the foot and mouth viral coat into live human adenoviruses. When animals get this injection, infected cells produce the foot and mouth viral coat and trigger an immune response. The adenoviruses themselves cannot replicate.

Initial tests show that this vaccine works as well as conventional vaccines, Grubman says. "One shot confers protection after seven days." Crucially, the adenovirus contains the genes for only a few of the foot and mouth viral proteins. So testing blood for antibodies to the missing viral proteins can easily distinguish between vaccinated and infected animals.

Ring vaccination

Grubman says that such a "marker vaccine" could be used to ring vaccinate animals in countries such as the US and Britain in the event of an outbreak. You could then test vaccinated animals regularly to see if they have been exposed to the wild virus. If none is found, the country could be declared disease-free.

"It should be considerably cheaper than paying farmers for the cost of slaughter," Grubman says. And because the vaccine contains live rather than attenuated viruses, its effect may be longer-lasting.

Other researchers are working on similar new vaccines, such as those at the Institute for Animal Science and Health in Lelystad, The Netherlands, but the vaccines will not reach the market soon. And even when they do, the disease could still spread during the seven-day delay before protection kicks in. For the moment, it looks as if the slaughter will continue.

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